Overall it could be A LOT of things (however I do not see or know your side of this so forgive me please).

The best thing I can really think of is look to the DIYers so anything where they can do something new, or simplify a project. so here are "my" (note my mental thinking just because I work on cars as a hobby) ideas. I do realize covering all aspects(ex: Ford Mustang, Chevy Camaro, Dodge Challenger, Nissan Z-series, etc.) isn't logical but generalized things can be acheived (I think, you can prove me wrong):

Archangel416 I would like to see car electronics, such as and not limited to LED interior and exterior lights, HID Bulbs, COBB/Hondata tuning Modules, RADARs. You can also include accessories such as Plastidip, Autodip, and or 3M Vinly wraps. Anything that is not specific to a certain brand of cars. it would not make sense to have something specific to a certain type of a car.

I agree, however there a lot of mods out on the market that can be spread beyond certain car brands (ex: Turbos, Exhaust kits (like all the tubing not aka universals), Seats, Seat deletes, or even 3rd party or stand alone ECUs (or whatever your preference to call it).

There are a handful of things many state is for only one vehicle but true car enthusiasts know better (like the old joke of if it has an engine bay someone will try and LS swap). Overall I do agree with you.